Dimeric fatty acids



DIMERIC FATTY ACIDS Stuart A. Harrison and Kirtland E. McCaleb,Minneapolis, Minn., assignors to General Mills, Inc, a corporation ofDelaware No Drawing. Application August 1, 1951, Serial No. 239,846

4 Claims. (Cl. ZEN-46?) The present invention relates to a novel processof producing dimeric fatty acids and esters thereof, and to theresultant products. Polyesters, polyamides, and other derivatives ofthese dimeric fatty acids possess unusual properties which distinguishthem from correspond ing products derived from other dimeric fattyacids. The dimeric fatty acids of the present invention are useful inthe coating, resin, and fiber fields.

The present invention involves the dimerization of monoolefinic higherfatty acids to produce dimeric, and, to some extent, higher polmericacids, which retain the unsaturation of the fatty acids from which theyare derived. It is thus possible to produce dimeric acids from suchunsaturated acids as oleic acid, which do not readily undergopolymerization in the usual thermal polymerization process. In addition,any polymers formed in the usual thermal polymerization of oleic acidare essentially saturated or contain one double bond per dimer molecule,whereas the polymeric acids of the present invention retain theunsaturation of the fatty acids employed.

It is therefore an object of the present invention to provide a novelprocess of producing dimeric fatty acids and esters thereof frommono-olefinic fatty acids, the polymeric acids retaining theunsaturation of the fatty acid starting material.

It is also an object of the present invention to provide novel dimerichigher fatty compounds derived from mono-olefinic acids and containingin the dimer the unsaturation of the original fatty acid.

The process involves the treatment, at temperatures in excess of 50 C.,of higher fatty acids or esters thereof having only one double bond inthe fatty group, with organic peroxides having the formula ROOR in whichR is a tertiary alkyl group and R is selected from the group consistingof tertiary alkyl and tertiary alkyl peroxyalkyl groups. Typical ofthese peroxides are di-tertiary butyl peroxide; 2,2-bis-t-butylperoxypropane; 2,2-bis-t-butylperoxy butane; 2,2-bis-t-butylperoxy pentane;and 3,3-bist-butylperoxy pentane. The process is applicable to the freefatty acids containing from 8 to 22 carbon atoms, to the lower aliphaticesters thereof, as for example, the methyl esters, and to the polyhydricalcohol esters thereof, as for example, the glycerides and thepentaerythritol esters. Any higher fatty acid containing a single pointof unsaturation may be employed in the present process. Commerciallyoleic acid is the principal acid readily available for this purpose, andaccordingly the invention will be described with particular referencethereto.

The process involves merely mixing thefatty acid or its ester with theperoxide, and heating the mixture in an inert atmosphere for therequired time at the required States atent O "ice temperature. In orderto reduce the time period to a commercially practical point,temperatures in excess of C. are usually employed. Preferably thetemper: atures are in the neighborhood of -l50 C., requiring timeperiods of 12 to 48 hours. At the completion of the reaction period, thereaction product may, if desired, be stripped under vacuum to remove allthe decomposition products of the peroxide as well as any monomericfatty acids or esters present therein. The resultant prodnot isessentially a dimeric acid or dimeric ester and contains smallerquantities of higher polymers. It will be appreciated that the removalof the decomposition prodnets and the monomeric fatty acids or esters isnot essential if the product desired is a mixture of monomer and dimerand higher polymers.

Example The oleic acid employed in this example had an acid number of198.4, and an iodine number of 88.7. 20 grams (0.971 mol) of this oleicacid and 0.75 g. (0.0051 moi) di-tertiary-butyl peroxide were heatedwithout agitation in sealed bottles under nitrogen. The temperature wasmaintained at 130 C. for 24 hours. Then an additional 0.75 g. ofdi-tert-butyl peroxide was added, and the heating was continued foranother 24 hours. The reaction mixture was then stripped under vacuum toremove volatile decomposition products. The rcsidue was distilled underhigh vacuum to remove monomeric acid and to yield a dimeric fraction anda polymeric residue. The following properties were found for the dimericfraction (theoretical values for a dimer containing two nonconjugateddouble bonds per molecule of dimer acid are given in parentheses):molecular weight 548 (565); acid number 186.5 (198); iodine number(Rapid Wijs) 91.7 (89.9); spot at 231m 5.6 (0). This ultravioletabsorption may be due to the presence of a small amount of a conjugatedisomer such as (1) below.

Thus it appears that the dimeric material is largely a dimer acid ofoleic acid having retained the unsaturation of the original oleic acid.Possible structures for this type of product are the following:

The reaction with the monohydric and polyhydric alcohol esters ofmono-olefinic acids proceeds in the same manner and under the sameconditions described with reference to the free acid in the example.Similarly, any of the peroxides listed above can be substituted for theditertiary-butyl peroxide in the example and the process conducted underthe same conditions to produce similar results.

The quantity of peroxide may vary quite widely. The amount of polymerformed appears to be directly proportional to the amount of peroxideemployed. If very small quantities are used small quantities of polymerare formed and it may be necessary to strip off large quantities ofmonomer to obtain a relatively pure or high concentration polymer. Wherelarge quantities of peroxide are employed, there is some tendency forthe formation of trimers and higher polymers. In general, from about 5mol percent to 30 mol percent is preferred. Quantities outside thisrange may be used with the general eifect on results described above.

We claim as our invention:

1. Process of dimerizing a compound selected from the group consistingof higher fatty acids containing only one double bond. and loweraliphatic monohydric alcohol esters thereof, which comprises heatingsaid compound to a temperature in excess of 100 C. in the presence oforganic peroxide having the formula ROOR in which R is a tertiary alkylsgroup and R is selected from the group consisting of tertiary alkyl andtertiary alkyl peroxyalkyl r p n i 2. Process of dimerizing a compoundselected from the oup consisting of higher fatty acids containing onlyone double bond, and lower aliphatic monohydric alcohol esters thereof,which comprises heating said compound to a temperature in excess of 100C. in the presence of di-tertiary-butyl peroxide.

3. Process of dimerizing oleic acid which comprises heating oleic acidto a temperature in excess of 100 C. in the presence ofdi-tertiary-butyl peroxide.

4. Process of dimerizing oleic acid which comprises heating cleic acidto a temperature in the range of 130- 150 C. in the presence ofdi-tertiary-butyl peroxide.

References Cited in the file of this patent UNITED STATES PATENTSWhetstone et a1. Sept. 18, 1951 Wiebe Mar. 11, 1952 OTHER REFERENCES

1. PROCESS OF DIMERIZING A COMPOUND SELECTED FROM THE GROUP CONSISTINGOF HIGHER FATTY ACIDS CONTAINING ONLY ONE DOUBLE BOND, AND LOWERALIPHATIC MONOHYDRIC ALOCHOL ESTERS THEREOF, WHICH COMPRISES HEATINGSAID COMPOUND TO A TEMPERATURE IN EXCESS OF 100*C. IN THE PRESENCE OFORGANIC PEROXIDE HAVING THE FORMULA ROOR1 IN WHICH R CONSISTING OFTERTIARY ALKYL AND TERITARY ALKYL PEROXYALKYL GROUPS.